Swedish and Danish census and hospital discharge data, linked for follow-up to cancer, mortality, and population registries, were used to assess cancer risk among individuals with specific medical and occupational exposures. Danish patients with systemic lupus erythematosus were at increased risk of lymphoma, lung cancer, liver cancer, and rare female genital cancers. These cancer excesses were similar to those found among Danish patients with rheumatoid arthritis. Patients in both Sweden and Denmark undergoing tonsillectomy before the age of 12, were found to have an increased risk of Hodgkin's disease. Alternatively, appendectomy in Denmark was not associated with an excess of any cancer. Silicotic patients in both Sweden and Denmark were at increased risk of lung cancer, and mortality from tuberculosis, non-malignant respiratory conditions, and autoimmune musculoskeletal disorders. Patients with porphyria in both Sweden and Denmark had an increased risk of liver cancer, lung cancer, and mortality from non-malignant respiratory conditions. Diabetic patients in both Sweden and Denmark were found to be at increased risk of cancers of the liver, pancreas, kidney, endometrium, colon, and lymphoma. Swedish patients with hemochromatosis had a cumulative risk of hepatic cancer of 10% after about nine years. Patients with endometriosis had increased risks of lymphoma and breast and ovarian cancers, but not cervical or endometrial cancer. The diagnosis of venous thromboembolism was found in Sweden to precede by a considerable time interval (more than ten years) the diagnosis of a wide variety of cancers occurring in excess. No excess of brain tumors was seen from 1-15 years after hospitalization for serious head trauma in Denmark except for one rare type, intracranial vascular tumors. Patients hospitalized in Sweden for kidney or ureter stones were at increased risk of cancers of the bladder and renal pelvis, but not renal cell cancer. Preliminary analyses of Swedish census data have found an increased risk of endometrial cancer for women with sedentary occupations. Swedish census data also revealed an increased risk of lymphoma associated with residence in Southern versus Northern Sweden, however outdoor occupations were not associated with increased risk.